An interesting concept for a Percy Jackson God OC fanfiction could be an OC who was created by the gods as an experiment. This OC would have powers that are a combination of different gods' powers, but they are also an outcast among both gods and demigods because of their origin. They might struggle to find their place in the world and go on a journey to discover who they really are and what their purpose is. Along the way, they could form unlikely alliances with both demigods and minor gods who also feel like outsiders.
Another interesting concept is an SI OC who is from a different time period, like the Middle Ages. They would have to adapt to the modern world of Percy Jackson while also using their archaic knowledge and skills to their advantage. Maybe they know ancient battle tactics that are useful against the Titans or Giants. They could also introduce medieval weaponry and fighting styles to Camp Half - Blood.
Another plot could involve an OC who is a child of a minor god that has been overlooked by the Camp Half - Blood community. This OC, with Percy's help, tries to prove the importance of their godly heritage and ends up uncovering a long - lost prophecy related to their parent god. This would lead to an adventure full of self - discovery and challenges for both the OC and Percy.
One idea could be an OC with the power to control water in unique ways, like creating ice sculptures that can come to life. Another could be an OC who has the magic to communicate with mythical animals and use them as allies. Maybe an OC with magic that allows them to manipulate time on a small scale, like freezing time for a few seconds during a battle.
One idea could be exploring how Percy discovers he has a connection to the first god that no one else knows about. Maybe he has strange dreams that lead him on a quest to uncover the secrets of this primordial deity.
One idea could be that the OC is a new camper at Camp Half - Blood. She has a special power that Percy is intrigued by. They start off as friends, helping each other in various quests. As time goes on, they realize their feelings for each other during a particularly dangerous quest where they have to rely on each other completely.
Perhaps in the fanfiction, the Elder Gods start to interfere with the modern world of demigods more directly. Percy and his friends notice strange phenomena, like the weather going haywire and magic behaving erratically. They soon find out it's because an Elder God is trying to regain its former power and is using the chaos to break through the barriers that keep it in a weakened state. Percy then has to find a way to stop it by using his unique connection to water and the help of his father, Poseidon.
One idea could be Percy having to face a new type of demon that is immune to water, his usual weapon. So he has to find a new way to fight. Another could be Percy being tricked into serving the God of Demons for a while and then realizing his mistake and trying to break free.
One idea could be exploring a new adventure where Percy has to team up with a minor god that has been forgotten. They could go on a quest to regain the forgotten god's power and status in the pantheon.
Perhaps Percy, as the God of Wisdom, has to deal with a situation where his wisdom is being questioned by the other gods. They don't believe that a former hero like him can handle the responsibilities of wisdom. So he has to prove himself by solving a complex problem that has been plaguing Olympus for centuries. He uses his unique perspective as a demigod - turned - god to come up with a solution that no one else could think of.
One idea could be Percy having to prove his divinity in a new way. Maybe he has to face a trial set by the gods where he can't use his usual powers but has to rely on his wits and faith. Another could be Percy interacting with a different pantheon's deities who mistake him for one of their own sons of god. He'd have to navigate their culture and rules.